Coaxial microwave diode and method of making the same



May 2, 1961 2,982,894

CQAXI AL MICROWAVE DIODE AND METHOD OF MAKING THE SAME Filed Jan. 12, 1960 INVENTOR, moms c. TWEED/E, JR.

BYWMW A TTOR/VEX good electrical conductor.

COAXIAL MICROWAVE DIODE AND METHOD 013' MAKING THE SAME Thomas 'C. Tweedie, Jr., Philadelphia, Pa, asslgnor to the United States of America as represented by the S'ecrelaryofthe Army Filed In. 12, 1960, Ser. No. 2,0 3' Claims- (Cl. 317-236) This invention relates to seals and is particularly concerned with an hermetic seal between the bead and the outer conductor of a coaxial microwave diode and a method of making same.

Many attempts have been made to prepare an hermetic seal between the bead and the outer conductor of a coaxial cartridge. Heretofore, in coaxial microwave diode cartridges the whisker and inner conductor assembly is mounted on a molded insulating bead that is pressed into the outer cylinder and secured by a crimp in the outer conductor. The use of such seal has, however, raised an unexpected problem, because at microwave frequencies it has permitted electrical contaminants to enter the region of whisker to semiconductor material contact.

It is accordingly an object of the present invention to provide a method of making an hermetic seal for a coaxial microwave diode.

Another object of this invention is to provide an hermetic seal between the bead and the outer conductor of a coaxial microwave diode.

In accordance with the present invention there is provided a method for preparing an hermetic seal between the bead and the outer conductor of a coaxial microwave diode which comprises cutting the inner liner of a section of duplex tubing into three sections, one of which the size of the bead is discarded, the other two sections along with the bead are placed into theexternal section of the duplex tubing and soldered.

-cally sealed to the inner surface of said outer tube and to the opposing ends of the tubular elements.

For a more detailed description of the invention, together with other and further objects thereof, reference is bad to the following description taken in connection with the accompanying drawing, which is a sectional view of a semiconductor coaxial microwave diode embodying the .invention.

Referring to the drawing, there is shown a coaxial microwave diode cartridge having a cylindrical metal outer conductor 12, preferably of cupro-nickcl or other- Extending coaxially within and abutting the inner surface of tube 12 are a pair of longitudinally spaced conductive tubular elements 14 and 16, preferably of silver. Intermediate elements 14 and 16 is an annular ceramic bead 18 having its outer cylindrical surface 20 coated with a metal layer and in abutment with the inner surface of outer conductor 12. A coating of solder 22 around the metalliud surface 20 bonds bead 18 to the inner surface of conductor 12 and to the opposing ends of elements 14 and 16, yielding a Patented May 2, 1961 ice desired hermetic seal between the bead and the outer conductor. v I

Extendingcoaxially-through. ceramic bead 18 there is' provided a centrally positioned inner conductor 24 sealed thereto. Attached to the upper end of inner conductor 24, as shown in thedrawing, is a tungsten whisker bent into a loop and having an electromechanically pointed end 31. Spaced from the upper end of inner conductor 24- and hermetically sealed within tubular element 14 is a metal conductive plug 28 having fastened .to its lower end a semiconductor wafer 26, preferably silicon. In fabrication, plug 28 and its associated semiconductor wafer 26 is advanced until the wafer makes contact with the pointed end 31 of whisker 30, Plug 30 serves to complete the enclosure of an hermetically sealed cavity 32, within tubular element 14, containing wafer 26 and whisker 30. A metal cover 34, in the shape of a can having a bottom opening, is sealed to the outer surface of tube 12 and further seals cavity 32.

The hermetic seal between bead 18 and outer conductor 12 is prepared in the following manner:

The inner silver liner of a cupro-nickel duplex tube having a diameter equal to that of bead 18 is first removed. The external portion'of the duplex tube is outer conductor 12. A mid-section of such inner liner of such lengthequal to the longitudinal length of bead 18, is cut away, leaving end sections 14 and 16. Metallized head 18, which has had its surface 20 coated with solder 22, is then placed between and in abutment with the end sections 14 and 16 so that the resultant structure is identical in length to the original inner liner. Thethree contiguous portions, end sections 14 and 16 and bead 18, are then inserted into outer conductor 12 in abutment therewith. Heat, in. any suitable fashion, is applied to the complete assembly to such a degree to cause solder 22 to flow thereby bonding elements 12, 14, 16 and 18 to form an hermetically sealed unitary structure.

while there has been described what is at present con-v sidered a preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is therefore aimed in the appended claims to cover all such changes andmodifications as fall within the spirit and scope of the invention.

What is claimed is: 1

1. A coaxial microwave diode comprising an outer conductor, an inner conductor extending therethrough, an insulating bead within and contacting said --outer conductor, said inner conductor passing through said bead and sealed thereto, a pair of longitudinally spaced conductive tubular elements extending coaxially within and in abutment with the inner surface of said outer conductor, said bead having a metallic coating on its outer surface where it contacts said outer conductor and being intermediate said tubular elements and in contact therewith, a layer of sealing material intermediate the outer surface of said bead and the outer conductor to form an hermetic seal between said bead and said outer conductor.

2..A coaxial microwave diode having an outer conductor, an inner conductor extending therethrough, an

doctor and the other end in point contact with said semiface of said head and the outer conductor to form an conductor body. f th fur hermetic seal between said bead and said outer conductor.

3. A device of the kind set or in claim 2' and ther including a pair of longitudinally spacedconductive Rafael-1m Cited m the me of am pawn tubular elements'extending-coaxially within and inabut 5' UNITED STATES PATENTS ment .with said-outer conductor, said bead having a 2,813,326 Liebowitz Nov. 19, 1957 metallic coating on its outer surface where it contacts r 2,836,878 Shepard -June 3, 1958 said outer conductor and being intermediate said tubular 2,906,930 Raithel Sept. 29, 1959 elements, a layer 'of solder intermediate the outer sur- 2,917,684 Becherer Dec. 15, 1959 

